Tape Tool does work on Toonz Raster levels.
You have to select the appropriate parameters to see it at work, though.
Pay close attention to the Distance used (this distance also depends on the zoom level you're using, zoom back to ensure it actually closes the gap as expected). Also, if you want to see the line created, raise the Opacity value to 255 (normally the line created will be transparent, nonetheless it will close the area, and it will be fillable).
To make sure the closing is actually working as desired, you can enable View > Fill Check, where you can see the fillable areas as grey areas (no matter if they are actually filled of are just potentially fillable areas).